The invention relates generally to safety belt retractors, and more particularly to a locking retractor.
A typical safety belt retractor includes a rotatable reel on which a safety belt is wound and a spring for urging rotation of the reel in a predetermined direction. The spring permits the reel to rotate so that the belt may be protracted for use, and retracts the belt after use. In a locking retractor, a locking mechanism prevents unwinding of the belt during rapid acceleration or deceleration of the vehicle, as due to a collision.
In one known type of locking mechanism, locking of the reel is effected by a first ratchet and pawl cooperating to bring a second ratchet and pawl into locking engagement. In response to rapid acceleration or deceleration, an inertial sensor displaces the first pawl into engagement with the first ratchet. The first ratchet is rotated by protraction of the belt, causing further displacement of the first pawl, which results in displacement of the second pawl into locking engagement with the second ratchet wheel, thereby preventing further rotation of the reel, as both ratchet wheels are typically fixed to a common shaft with the reel. In the above-described mechanism, the first ratchet and pawl are lightweight, as their function is merely to displace the second pawl. The second pawl and ratchet are heavier, as they are designed to withstand the stress resulting from the restraining function of the belt. If the second pawl engages the tip of one of the teeth on the second ratchet in such a manner that the second ratchet can continue to turn, but the second pawl is momentarily constrained, the first pawl and ratchet may be subjected to stress in excess of their strength, resulting in failure of one or both. In the past this problem has been addressed by attempting to maintain a timed relationship between the two ratchet wheels so that when the second pawl is displaced it does not engage the tip of a rachet tooth but rather enters between a pair of adjacent teeth.
The present invention provides a novel solution to the above problem which avoids any need to maintain a timed relationship between the respective ratchet wheels.